Management system for the operation of a wind turbine

ABSTRACT

The invention relates to a management system for the operation of a wind turbine, which regulates the power output of the turbine. The wind turbine includes a rotor with at least one rotor blade that is positioned at an adjustable angle to the rotor. The management system regulates the rotor speed within a predefined wind speed range by varying the rotor blade angle in order to set a nominal output and reduces the output in excess of a defined wind-speed-dependent threshold value. The threshold value is a defined rotor blade limiting angle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a management system for the operation of a windturbine, which regulates the power output of the turbine.

2. Description of Related Art

Generic management systems are used in wind turbines comprising a rotorwith at least one rotor blade, wherein the rotor blade is positioned atan adjustable angle to the rotor. The management system regulates therotor speed within a predefined wind speed range by varying the rotorblade angle in order to set a nominal output.

If a wind turbine is operated while wind speeds are too high, theturbine may be destroyed by the high mechanical load. For that reason,generic management systems are designed such that they turn off theturbine in excess of a defined turn-off wind speed, wherein the turbineis preferably not turned off in an abrupt manner, but by slowly reducingthe output. For example, a generic management system is disclosed in DE195 32 409 A1.

DE 198 44 258 A1 also discloses a management system which is used toreduce the output as soon as the wind speed reaches a predefined value.Herein, reduction in output is also achieved by varying the rotor bladeangle. However, reduction in output is already initiated when a windspeed threshold value is reached, wherein the wind speed threshold valueis lower than the turn-off wind speed.

The reduction in output is intended to reduce the mechanical loadexerted on the turbine, wherein said mechanical load rises withincreasing wind speed; thereby, the turbine can be designed with lesspowerful dimensions, thus also permitting lowering of costs.

Both of the management systems described above start to reduce theoutput as soon as a defined wind-speed-dependent threshold value isreached. Said threshold value is based on the wind speed measured.Usually, the wind speed is measured by means of a nacelle anemometer.This measurement method is relatively inaccurate and, thus, fails toprovide a good indicator of the load exerted on the turbine.

For that reason, the threshold value in excess of which the managementsystem reduces the output a wind turbine should not be based on the windspeed measured but on an input variable that can be determined moreeasily, both physically and with regard to the controller used.

BRIEF SUMMARY OF THE INVENTION

The present invention aims at creating a management system that uses athreshold value with the features mentioned above.

This problem is solved by a management system comprising the elements ofClaim 1.

As is the case with the generic management system, the management systemaccording to the invention is also used in wind turbines which comprisea rotor with adjustable rotor blades, wherein the management system isdesigned such that it regulates the rotor speed within a predefined windspeed range by varying the rotor blade angle in order to set a nominaloutput.

To this end, the rotor blade angle is increased once the nominal speedis reached with increasing wind speed, whereby the nominal speed and,thus, the nominal output as well can be maintained despite increasingwind speed, as has already been described above. The management systemstarts to reduce the output as soon as a defined wind-speed-dependentthreshold value is reached.

Therein, the management system according to the invention uses a definedrotor blade limiting angle as threshold value. Said rotor blade limitingangle is the rotor blade angle that results at a wind forcecorresponding to the turn-off wind speed and is used to set the nominaloutput. The rotor blade limiting angle is depending on the particularrotor blade used and can be determined empirically by measurementsand/or simulations.

Using the rotor blade limiting angle as threshold value is to advantagein that it is an input variable that can be determined easily by thecontroller used, because the rotor blade angle is already known from theset nominal output. Furthermore, the rotor blade limiting angle is adirect indicator of the current load exerted on the turbine, thusrepresenting an input variable for the reduction of said load that ismore reliable than the indirectly measured wind speed.

In a preferred embodiment of the invention, the present managementsystem according to Claim 2 is designed such that the output is reducedby further varying the rotor blade angle once the rotor blade limitingangle is exceeded. Herein, the angle of the rotor blade to the rotor isincreased according to Claim 3.

This is to advantage in that the turbine is not turned off promptly whenthe turn-off wind speed is reached, but the power output is reducedslowly until a turn-off output is reached and the turbine can bedisconnected from the power supply. On the one hand, this procedureprovides the advantage of a better compatibility with the external powersupply system. On the other hand, it allows an extended power curve andan improved energy yield.

In a further preferred embodiment, the present management systemaccording to Claim 4 is designed such that the rotor blade angle ismaintained at a largely constant value until the nominal output isreached.

After the nominal output has been reached, the present management systemaccording to Claim 4 is designed such that the rotor blade angle is setin relation to the wind speed, i.e. the rotor blade angle is increasedor reduced depending on the wind speed value, in order to maintain thenominal output at a constant value.

The management system according to the invention regulates the poweroutput of a wind turbine in excess of the turn-off speed in anadvantageous manner, i.e. in relation to the rotor blade angle only. Anyadditional measurement variables, such as the wind speed which, owing tounfavorable conditions, can be determined only difficultly and are,therefore, often inaccurate, are not necessary any longer.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, the invention will be illustrated in more detail by means of twofigures. In the figures:

FIG. 1 is a front view of a wind turbine; and

FIG. 2 is a schematic diagram representing the regulation of the nominaloutput in relation to the rotor blade angle.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is the top view of a wind turbine (1) with a tower (2) that isset up on the ground and at the top of which a rotatable nacelle carriesa rotor (3) that rotates about a horizontal axis and comprises threerotor blades (5), wherein said rotor blades are positioned at anadjustable angle to the rotor.

FIG. 2 is a schematic diagram representing the regulation of the nominaloutput in relation to the rotor blade angle, wherein it is assumed thatthe wind speed is rising steadily.

At point 1 in FIG. 2, the turbine starts running. Between point 1 andpoint 2, the turbine follows a torque-speed characteristic of agenerator provided in the turbine, until the nominal output is reached.The rotor blade angle is not changed in this stage. At point 2, theturbine has reached the nominal output.

Once point 2 has been exceeded, the wind speed is higher than necessaryfor generating the nominal output; for that reason, the managementsystem starts to regulate the output via the rotor blade angle. Toachieve this, the management system increases the rotor blade angle,whereby the lift of the rotor blades is lowered and the rotor speed and,thus, the output is reduced. As a result, a constant nominal power canbe output by varying the rotor blade angle.

As shown between points 2 and 3 in FIG. 2, the rotor blade angle issteadily increased with rising wind speed to ensure that the nominaloutput of the turbine remains at a constant value. At point 3, the windspeed reaches a value where the management system adjusts the rotorblade to an angle corresponding to a limiting angle represented in FIG.2. Once the limiting angle is exceeded, the management system starts toreduce the output of the turbine. To achieve this, the rotor blade angleis increased such that the power output is steadily reduced until theturbine reaches a turn-off output as shown at point 4 in FIG. 2.

In further embodiments of the invention, the output can also be reducedin a different manner, for example in the form of steps orexponentially.

1. A management system for the operation of a wind turbine whichregulates the power output of the turbine, wherein the wind turbinecomprises a rotor with at least one rotor blade that is positioned at anadjustable angle to the rotor and wherein the management systemregulates the rotor speed within a predefined wind speed range byvarying the rotor blade angle in order to set a nominal output andreduces the output in excess of a defined wind-speed-dependent thresholdvalue, and wherein the threshold value is a defined rotor blade limitingangle.
 2. A management system according to claim 1, wherein themanagement system varies the rotor blade angle in order to reduce theoutput.
 3. A management system according to claim 2, wherein themanagement system increases the rotor blade angle in order to reduce theoutput.
 4. A management system according to claim 1, wherein themanagement system maintains the rotor blade angle at a constant valueuntil the nominal output is reached.
 5. A management system according toclaim 1, wherein once the nominal output has been reached, themanagement system adjusts the rotor blade angle in relation to the windspeed in order to maintain the nominal output at a constant value.
 6. Amethod of regulating the power output of a wind turbine having at leastone rotor blade that is positioned at an adjustable angle to the rotorcomprising the steps of: regulating the rotor speed within a predefinedwind speed range by varying the rotor blade angle in order to set anominal output; and reducing the output in excess of a definedwind-speed-dependent threshold value wherein the threshold value is adefined rotor blade limiting angle.